Rolling silicon-iron



tion, East Pittsburg Pa., a corporation of Pennsyl- Vania No Drawing. Filed Nov. 6, 1957, Ser. No. 694,709 4 Claims. (Cl. 80-60) This invention relates to normally brittle silicon-iron alloys, and in particular it concerns a method of rolling such alloys to thin gauges.

Silicon-iron alloys with a silicon content in excess of 4.5 percent are of interest to the electrical industry in view of their reported excellent magnetic properties and very low magnetostriction. To use such material successfully and efliciently it is necessary to be able to fabricate the alloy with sufiicient ease for commercial adaptation to produce the shapes desired for various electrical applications. Fabrication of these alloys, such as the 6.5 percent silicon-iron alloy, to very thin tapm has not been previously accomplished due to its extreme brittleness. The ductility of the alloy as shown by the reduction in area and elongation determined in a tensile test, is zero or nearly zero. Other mechanical properties, such as the tensile strength, also are very poor.

It is therefore a primary object of the present invention to provide a method by which silicon-iron alloys containing at least 4.5 weight percent of silicon can be readily rolled to tapes suitable for use in electrical applications.

Heretofore attempts to roll alloys of this general type have been made. For example, it had been thought that by quenching a silicon-iron alloy from above its orderdisorder temperature, ordering reactions would be suppressed and the resulting material would be ductile enough to permit cold rolling. This idea was premised on the similar and effective treatment of cobalt-iron alloys. When attempts to use this procedure with silicon-irons were made, however, it was found that the alloy cracked severely on quenching.

It has been reported that the 6.4 percent silicon-iron has been rolled at a temperature of 575 C. to 7 to 15 mil thicknesses. The resulting product, however, was very brittle and could not be cold rolled or cold punched. Consequently, it would not be possible to use that procedure commercially unless the as-rolled product was in a usable shape; that normally can not be accomplished.

in accordance with our discoveries these alloys can be rolled to produce a material having a structure which will permit subsequent cold rolling or other cold forming or deforming without destroying the material. This desirable result is achieved by rolling an alloy of an intermediate thickness at a moderately elevated temperature, hereinafter described, to a sheet, The resulting sheet is characterized by an elongated microstructure and is duetile; accordingly, it can be cold rolled at room temperature to any desired gauge. In this manner we are able to roll, for example, 6.5 percent silicon-iron to ductile tape of one mil thickness or less.

In practicing our invention an ingot, or slab, of the alloy is first hot rolled to a plate of a thickness on the order of 110 mils or thinner. We have rolled the material within the range of about 750 to 850 C. with satisfactory results. While any rolling apparatus desired may be used, We have found it suitable to use a two high mill Where these larger thicknesses are involved. A plurality of passes is made to effect the necessary reduction. Every few passes the material is reheated, if necessary, in order to insure that the desired rolling temperature is maintained. Consequently, the alloy temperature rarely departs much from the rolling temperature. Since the fitates Patent lice structure desired for cold-rolling is not produced during hot rolling, because of recrystallization, it is apparent that hot rolling must not be extended to the point where there is too little thickness remaining to obtain that desired microstruoture.

Warm rolling is conducted on the strip resulting from the hot rolling step. The warm rolling temperature is materially above room temperature but suitably does not exceed 425 C., because we have found that rolling at higher temperatures, on the order of about 450 0.,

results in cracking. A temperature range that can be used for this step, with binary silicon-iron, is about 350 to 425 C. In the warm rolling procedure, the alloy is reduced to a thickness at least as low as about 25 mils. Here, too, Warm rolling to the larger thicknesses of, say, 30 to 35 mils has been found to be less desirable from the standpoint of subsequent cold rolling since undue cracking, particularly at the edges, may occur and the material may evidence only marginal ductility. In instances we have permitted the hot rolled product to cool to room temperature prior to warm rolling without deleteriously afiecting the properties. Accordingly, it is apparent that these respective steps need not follow one another promptly.

The strip obtained from the warm rolling step can then be cold rolled to the desired thickness. We have successfully cold rolled this material readily to l and 2 mil thick tapes many times. This result has been achieved Without experiencing edge cracks. Moreover the resultant cold-rolled tapeis very ductile. It may be sheared cold with no cracking and may be sent back on itself without breaking. Heretofore it was not unusual to drop materials of this general nature and find that they shattered as a consequence of their unusual brittleness.

The rolling steps of our invention can be carried out with any rolling equipment desired. For example, twohigh or four-high mills may be used. All thin gauges, particularly below 10 to 15 mils thickness, a Sendzimir mill or its equivalent may be used for cold rolling. Similarly, the reductions per pass during each of the rolling steps is determined by the convenience of the operator and the equipment that is available to him. In our practice we have taken difierent reductions on the same sheet and have changed mills during a rolling procedure without adversely aifecting the results.

Our invention is primarily concerned with silicon-irons containing about 4.5 to 7.5 or more weight percent or silicon. Preferably the alloys contain 6 to 7 weight percent of silicon and the remainder iron. For the end uses contemplated, that is for various electrical applications,

the alloys suitably are made from electrolytic iron and commercial grade silicon. Other alloying constituents and impurities in conventional amounts may be present as long as they do not deleteriously interfere with the desired end results. In tact, certain alloying constituents such, for example, as aluminum, can be substituted for small amounts of the silicon with a distinct advantage in spreading the warm rolling temperature. For example the 6.5 weight percent silicon-iron generally is warm rolled within the temperature range of 350 to 425 C. When 0.5 weight percent of aluminum is substituted for an equal amount of silicon, the range of rolling temperature becomes extended at least to the lower temperature of 275 C. It may be expected that other ternary additions will produce a similar result.

The alloys can be prepared for use in this invention in any manner desired. Vacuum and controlled atmosphere procedures have been found of use, in making materials to be used for electrical applications, to prevent the uncontrolled introduction of impurities into the melts.

The invention will be described further in conjunction 3 with the following example. It should be understood that the details given are by way of illustration and are not to be construed as limiting the invention.

Example 7 An ingot was prepared from electrolytic iron and commercial silicon. A typical chemical analysis of these raw materials was within the following ranges:

Weight Percent Iron Silicon 98.5 min. .75 max.

.10 max. .03 max. Mg under .0O05

The raw materials, in a weight ratio of 93.5 parts of iron for each 6.5 parts of silicon, were charged to a vacuum induction melting furnace. The temperature of the furnace was raised and as the charge started to melt helium was admitted to prevent excessive evaporation of the silicon. An ingot having dimensions of l x 2 x 6 inches was poured under a helium atmosphere, was stripped hot and then was placed in a furnace containing a hydrogen atmosphere at 800 C'. The ingot was hot rolled at 800 C. with a two-high mill. To maintain the temperature of the material being rolled, a box furnace was located about 10 to 12 feet from the mill and the material fed thereto when required. The drop in temperature occurring upon transfer of the alloy from the furnace to the mill did not materially alter the rolling temperature. This hot rolling was performed at reductions of 50 to 75 mils per pass to a thickness of 100 mils.

The temperature of the sheet was then reduced to 400 C. [for warm rolling below the recrystallization temperature. Visual examination of the sheet at this point showed no edge cracks; it had a fine grain size which was nearly equiaxed. Warm rolling was conducted at 400 C., the temperature being maintained by a strip furnace 12 feet long .placed adjacent the entry end of the rolling mill. Since the furnace temperature was set at 400 C., the strip was rolled at almost exactly this temperature because it was pushed directly from the furnace through the rolls. Warm rolling continued at reductions of about 15 to milsper pass until the resulting material had a thickness of 20 mils, that is, about one fifth the original thickness. The reduction in thickness was 80%. This rolling procedure produced an elongated structure in the resulting strip. The strip was quite ductile and showed no significant edge cracking.

The 20 mil strip was then permitted to cool to room temperat-ure whereupon it was cold rolled to a thickness of 1 to 2 mils.

By the foregoing procedure we are able to obtain thin ductile tapes of the normally brittle silicon-iron without encountering serious edge cracking. The procedure followed in the above example can be readily practiced with existing commercially available equipment.

-'--For some applications it may be desirable to initiate cold rolling on strips on the order of mils thick or more. Where this is deemed necessary, the edges of the strip may be slit; in that manner nuclei that may cause edge crackings will be eliminated.

We have tested D.-C. magnetic properties of 6.5 percent silicon-iron tapes prepared according to our invention. The magnetic properties of the tapes were developed by annealing at an elevated temperature for short periods.

4 Representative data from these tests are as follows for 2 mil thick tape:

D.O. MAGNETIC PRoPER'llfilgiIoF 6.5 PERCENT SILICON- The excellent magnetic properties that may be developed in tapes obtained by our process make them particularly attractive for transformer and magnetic amplifier applications. They are of further interest because they may be used as a substitute for nickel-irons in many present applications with an apparent advantage in costs and efiiciency.

:In this specification, the term hot rolling is used in its usual sense of rolling at a temperature above the recrystallization temperature. Warm rolling indicates rolling at a temperature below the recrystallization temperature but above room temperature. Cold rolling indicates rolling at about room temperature.

The binary alloys of the present invention which contain from 4.5% to 7.5% by weight of silicon are characterized by high electrical resistivity. In the range of from 6% to 7% by Weight of silicon the magnetostriction is zero or nearly zero and therefore electrical apparatus made therefrom will be exceptionally quiet.

In accordance with the provisions of the patent statutes, We have explained the principle of our invention and have described what we now believe to represent its best embodiment. However, we desire to have it understood that the invention may be practiced otherwise than as specifically described.

We claim as our invention:

1. A method of producing thin gauge silicon-iron sheets of a thickness of the order of from 2 to 1 mils and less, comprising hot rolling an alloy plate consisting essentially of from at least 4.5 Weight percent to 7.5 weight percent of silicon and the remainder iron, to a thickness at least as thin as 110 mils, then Warm rolling the resulting material at an elevated temperature of above about 275 C. but below 425 C. to effect a reduction of about and the resulting material is at least as thin as about 25 mils to produce an elongated microstructure therein, and then, without annealing, rolling the resulting thin gauge material at about room temperature to effect a reduction of the order of to so that the cold rolled sheets are of the desired iinal thickness.

2. A method in accordance with claim 1 in which said hot-rolled plate is Warm rolled at a temperature of about 350 to 425 C.

3. A method of producing a relatively thick silicon-iron sheet that is ductile and capable of being directly cold rolled without annealing to a reduction of from 90% to 95 at about room temperature to thicknesses of the order of 2 to l mils and less which comprises warm rolling an alloy plate of a thickness of not over about mils and consisting essentially of at least 4.5 and not exceeding 7 .5 weight percent of silicon and the remainder iron, to at least as thin as 25 mils at an elevated temperature of above 275 C. but below 425 C.

4. A method according to claim 3 in which said plate is rolled at a temperature of 350 to 425 C.

References Cited in the file of this patent UNITED STATES PATENTS Cunningham "Dec. 16, 1913 Pil-ling Jan. 21, 1930 Otte Feb. 21, 1933 Detwiler May 30, 1933 6 Freeland Oct. 24, 1933 Goss June 22, 1937 Hiemenz Apr. 5, 1938 Reardon Mar. 18, 1941 Merrill Jan. 20, 1942 Cole et a1 Jan. 5, 1943 Littman June 14, 1949 

1. A METHOD OF PRODUCING THIN GAUGE SILICON-IRON SHEETS OF A THICKNESS OF THE ORDER OF FROM 2 TO 1 MILS AND LESS, COMPRISING HOT ROLLING AN ALLOY PLATE CONSISTING ESSENTIALLY OF FROM AT LEAST 4.5 WEIGHT PERCENT OF 7.5 WEIGHT PERCENT OF SILICON AND THE REMAINDER IRON, TO A THICKNESS AT LEAST AS THIN AS 110 MILS, THEN WARM ROLLING THE RESULTING MATERIAL AT AN ELEVATED TEMPERATURE OF ABOVE ABOUT 275* C. BUT BELOW 425*C. TO EFFECT A REDUCTION OF ABOUT 80% AND THE RESULTING MATERIAL IS AT LEAST AS THIN AS ABOUT 25 MILS TO PRODUCE AN ELONGATED MICROSTRUCTRUE THEREIN, AND THEN, WITHOUT ANNEALING, ROLLING THE RESULTING THIN GAUGE MATERIAL AT ABOUT ROOM TEMPERATURE TO EFFECT A REDUCTION ROF THE ORDER OF 90 TO 95% OS THAT THE COLD ROLLED SHEETS ARE OF THE DESIRED FINAL THICKNESS. 